This application claims the benefit of priority from the prior Japanese Patent Application No. 2000-275030, filed on Sep. 11, 2000; the entire contents of which are incorporated herein by reference.
1. Field of the Inventions
The present invention relates to a tunnel magnetoresistance effect device and to a portable personal device having a magnetic memory provided with said tunnel magnetoresistance effect device.
2. Discussion of the Background
A magnetoresistance effect element using a ferromagnetic thin film is used in, for instance, a magnetic head, a magnetic sensor, etc. Furthermore, a magnetic random access memory (MRAM) is recently proposed, which comprises a semiconductor substrate having formed thereon a magnetoresistance effect device. The MRAM is attracting attention as a next generation memory device promising high speed operation, high capacity, and non-volatile features.
In the magnetoresistance effect, the electric resistance of the ferromagnet itself changes with its direction of magnetization. Thus, a ferromagnet functions as a memory device because it can record information in accordance with the direction of its magnetization, and the information thus recorded can be read in accordance with the size of the electric resistance.
Recently, in a ferromagnetic tunnel junction having a sandwich structure comprising two ferromagnetic layers with a dielectric material inserted between them as a tunnel barrier layer, a magnetoresistivity ratio of 20% or higher is obtained by the tunnel magnetoresistance effect (TMR effect) (J. Appl. Phys., 79 (1996), p. 4724). A device having a ferromagnetic tunnel junction is denoted as a tunnel magnetoresistance effect device (TMR device).
In a TMR device, the direction of magnetization of one of the two ferromagnetic material layers sandwiching the tunnel barrier layer of dielectric material, i.e., the magnetization fixed layer, is fixed, and by changing the direction of magnetization of the other ferromagnetic layer that is in a magnetically non-coupled state with the magnetization fixed layer, i.e., the magnetization free layer in accordance with the applied external magnetic field, information of either xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d is recorded thereto. A TMR device having such a structure is called a xe2x80x9cspin-valve TMR devicexe2x80x9d.
To fix the direction of magnetization in the magnetization fixed layer, an antiferromagnetic material layer made of an antiferromagnetic material is provided in contact with the ferromagnetic layer to utilize the exchange coupling between the antiferromagnetic layer and the magnetization fixed layer.
FIG. 1 shows a cross sectional structure of a spin valve TMR device using an antiferromagnetic layer.
Referring to FIG. 1, the structure comprises an antiferromagnetic material layer 101 made of an antiferromagnetic material, having sequentially laminated thereon a magnetization fixed layer 102 made of a ferromagnetic material, a tunnel barrier layer 103 made of a dielectric material, and a magnetization free layer 104 made of a ferromagnetic material.
The magnetization of the magnetization fixed layer 102 is fixed in the direction indicated by an arrow A shown in FIG. 1 by the exchange coupling of the antiferromagnetic material layer 101. In contrast to this, the magnetization of the magnetization free layer 103 changes in accordance with an external magnetization field within a range indicated by arrows B and C shown in FIG. 1. As a result, the electric resistance of the TMR device yields a maximum when the direction of magnetization B of the magnetization free layer 104 is reversely parallel with the direction of magnetization A of the magnetization fixed layer 102, and yields a minimum when the direction of magnetization C of the magnetization free layer 104 is in parallel with the direction A.
A sense current for detecting the electric resistance of the TMR device is applied by a pair of electrodes connected to the upper and the lower planes (i.e., the upper plane of the magnetization free layer 104 and the lower plane of the antiferromagnetic material layer 101 shown in FIG. 1) of the TMR device. The direction of the sense current is perpendicular to the film plane of each of the layers.
The ferromagnetic material used in the magnetization free layer 104 and the magnetization fixed layer 102 is an alloy containing a magnetic metal selected from the group consisting of Co, Fe, and Ni. On the other hand, for the antiferromagnetic material that is used for the antiferromagnetic material layer 101, generally employed is an alloy containing Mn, such as IrMn, PtMn, RuRhMn, etc.
A process for producing a MRAM and the like by employing the TMR device above comprises a heat treatment in a temperature range of from about 300 to about 450xc2x0 C., such as a film deposition of an interlayer dielectric onto the SV-TMR device by means of CVD, a metal reflow treatment, etc. By applying such a heat treatment, Mn included in the antiferromagnetic material layer 101 of the TMR device easily diffuses into the magnetization fixed layer 102 and reaches the vicinity of the tunnel barrier layer 103. The diffused Mn then lowers the spin polarization ratio of the magnetization fixed ratio 102 and leads to a problematic decrease in magnetoresistivity ratio of the TMR device.
In order to prevent the lowering of the magnetoresistivity ratio from occurring, it has been suggested to insert a metallic layer made of a refractory metal, such as Ta, Ru, etc., into the magnetization fixed layer 102 (Appl. Phys. Lett., 76 (2000) 3792; and Appl. Phys. Lett., 76 (2000) 2424). However, as a result of the studies of the present inventors, it has been found that the metallic elements above cause grain boundary diffusion of Mn at temperatures of 300xc2x0 C. or higher, and that it is not possible to prevent the diffusion of Mn from occurring into the tunnel barrier layer.
Furthermore, it has also been suggested to insert a layer of a refractory metal into the interface between the antiferromagnetic material layer 101 and the magnetization fixed layer 102 (Appl. Phys. Lett., 76 (2000) 3792). However, as a result of the studies of the present inventors, it has been found that a refractory metal layer provided at the interface between the antiferromagnetic material layer 101 and the magnetization fixed layer 102 not only greatly impairs the fixing of the magnetization of the fixed layer 102, but also raises a concern that the refractory metal itself undergoes diffusion.
An object of the present invention is to provide a tunnel magnetoresistance effect device (TMR device) that is capable of effectively suppressing the diffusion of Mn from the antiferromagnetic material layer made of a Mn-based alloy into the tunnel barrier layer even in case of heat treatment, and yet, which exhibits superior device characteristics and thermal stability. Another object of the present invention is to provide a portable personal device equipped with such a TMR device.
In a first aspect, the present invention provides a tunnel magnetoresistance effect device comprising a first antiferromagnetic material layer containing manganese, a first magnetization fixed layer of ferromagnetic material disposed on the first antiferromagnetic material layer, a first inserted layer of an insulator material disposed on the first magnetization fixed layer, a second magnetization fixed layer of ferromagnetic material disposed on the first inserted layer, a first tunnel barrier layer of dielectric material disposed on the second magnetization fixed layer, and a magnetization free layer of ferromagnetic material disposed on the first tunnel barrier layer.
In a second aspect, a tunnel magnetoresistance effect device, comprises a first antiferromagnetic material layer containing manganese, a first magnetization fixed layer of ferromagnetic material disposed on the first antiferromagnetic material layer, a first inserted layer disposed on the first magnetization fixed layer and comprising MX, where M is an element selected from the group consisting of manganese, titanium, tantalum, vanadium, aluminum, europium, and scandium, and X is an element selected from the group consisting of oxygen, nitrogen, and carbon, a second magnetization fixed layer of ferromagnetic material on the first inserted layer, a first tunnel barrier layer of dielectric material on the second magnetization fixed layer, and a magnetization free layer of ferromagnetic material disposed on the first tunnel barrier layer.
In a third aspect, a tunnel magnetoresistance effect device comprises a first antiferromagnetic material layer containing manganese, a first magnetization fixed layer of ferromagnetic material on the first antiferromagnetic material layer, a first inserted layer on the first magnetization fixed layer and comprising NX, where N is a first element, X is a second element selected from the group consisting of oxygen, nitrogen, and carbon, and the bonding energy between the first and second elements is higher than the bonding energy between manganese and the second element, a second magnetization fixed layer of ferromagnetic material disposed on the first inserted layer, a first tunnel barrier layer of dielectric material on the second magnetization fixed layer, and a magnetization free layer of ferromagnetic material on the first tunnel barrier layer.
In a fourth aspect, a tunnel magnetoresistance effect device comprises a first antiferromagnetic material layer containing manganese, a first magnetization fixed layer of a first ferromagnetic material on the first antiferromagnetic material layer, a first inserted layer on the first magnetization fixed layer and comprising L1X, where L1 is a ferromagnetic element of the first ferromagnetic material or a ferromagnetic element of a second ferromagnetic material, and X is an element selected from the group consisting of oxygen, nitrogen, and carbon, a second magnetization fixed layer of the second ferromagnetic material disposed on the first inserted layer, a first tunnel barrier layer of ferromagnetic material on the second magnetization fixed layer, and a magnetization free layer of ferromagnetic material on the first tunnel barrier layer.
In a fifth aspect, a tunnel magnetoresistance effect deice comprises a first antiferromagnetic material layer containing manganese, a first magnetization fixed layer of ferromagnetic material and on the first antiferromagnetic material layer, a first inserted layer of an amorphous magnetic material on the first magnetization fixed layer, a second magnetization fixed layer of ferromagnetic material on the first inserted layer, a first tunnel barrier layer of dielectric material on the second magnetization fixed layer, and a magnetization free layer of ferromagnetic material on the first tunnel barrier layer.
Each of the magnetization fixed layers may have respective fixed magnetization that doesn""t substantially rotate in an applied magnetic field in which magnetization of the magnetization free layer does rotate.
In accordance with the invention as above, the diffusion of Mn from the antiferromagnetic material layer made of a Mn-based alloy into the tunnel barrier layer, even in case of heat treatment, can be effectively suppressed, and hence, a TMR device having superior device characteristics and thermal stability can be provided.
The TMR device above provides a magnetic memory device such as a MRAM when formed integrated on a semiconductor substrate and the like. The magnetic memory device can substitute conventional DRAMs, SRAMs, etc. Thus, a memory device obtained by integrating the TMR device according to the present invention can be mounted on a portable personal communication device such as a personal digital assistant, a portable personal computer, and a portable personal telephone (cellular phone), etc.
Furthermore, the TMR device according to the present invention can be applied to a magnetic sensor for reading out the magnetic information or a magnetic reproduction head (a magnetoresistance effect head). A magnetic reproduction head having mounted thereon the TMR device according to the present invention is also applicable to a magnetic reproduction device such as a hard disk drive.